Usetrace - Web app testing system that doesn’t require coding or constant updating

Visualping - Visualping is the easiest to use website checker, webpage change monitoring, website change detector and website change alert software of the web. Read more about Visualping.

BrowserStack - BrowserStack is a software testing platform for developers to comprehensively test websites and mobile applications for quality.

Distill Web Monitor - Distill is a web monitoring tool. It can monitor RSS feeds, a webpage or a part of webpage. Alerts in the form of pop-up, audio or emails can be received.

CrossBrowserTesting - Browser Testing made simple! Run automated, visual, and manual tests on 1500+ real browsers and mobile devices. Test more browsers, in less time.

Update Scanner - Update Scanner is a Firefox extension to monitor web pages for updates.